1. Field of the Invention
The present invention relates to a storage apparatus storing a license required to decrypt and reproduce encrypted data obtained using a data distribution system that allows copyright protection on copied information, particularly to a storage apparatus that allows copyright protection on information copied in a storage apparatus capable of multi-access.
2. Description of the Background Art
By virtue of the progress in digital information communication networks and the like such as the Internet in these few years, each user can now easily access network information through individual-oriented terminals employing a cellular phone or the like.
In such digital information communication networks, information is transmitted through digital signals. It is now possible to obtain copied music data and video data transmitted via the aforementioned information communication network without degradation in the audio quality and picture quality of the copied information, even in the case where the copying operation is performed by an individual user.
Thus, there is a possibility of the copyright of the copyright owner being significantly infringed unless some appropriate measures to protect copyrights are taken when contents subject to copyright protection such as music and image data are to be transmitted on the digital information communication network.
However, if copyright protection is given top priority so that distribution of content data through the disseminating digital information communication network is suppressed, the copyright owner who can essentially collect a predetermined copyright royalty for copies of a copyrighted data will also incur some disbenefit.
Sufficient measures must be taken in distributing content data such as music and image data to the public through the digital information communication network for the purpose of copyright protection since distribution per se is an act subject to restriction based on the copyright owner's right of transmission to the public.
In this state of affairs, it is necessary to prevent any unauthorized user from receiving content data transmitted to the public through a digital information communication network, as well as preventing any content data, once received by an authorized user, to be further copied without permission.
In view of the foregoing, a data distribution system is proposed in which a distribution server storing encrypted content data that is an encrypted version of content data distributes the encrypted content data via a terminal device such as cellular phone to a memory card loaded to the terminal device. In this data distribution system, a public encryption key of a memory card authenticated in advance by a certificate authority and a certificate thereof are transmitted to the distribution server when distribution of encrypted content data is requested. Upon confirming reception of the authorized certificate by the distribution server, the encrypted content data as well as the license required to decrypt the encrypted content data are transmitted to the memory card. The license includes a decryption key to decrypt encrypted content data (also called “content key” hereinafter), a license ID to identify the license, and control information to restrict usage of the license. When a license is to be transmitted from the distribution server to a memory card, the distribution server and memory card respectively generate session keys to exchange the keys between the distribution server and the memory card to establish an encryption communication path.
Eventually, the distribution server transmits the license to the memory card via the established encryption communication path. In the transmission process, the memory card stores the received encrypted content data and license in its internal memory.
When encrypted content data is to be reproduced, the memory card storing the encrypted content data and license is loaded to a terminal device that has a dedicated circuit. This dedicated circuit functions to read out the encrypted content data and content key from the memory card to decrypt and reproduce the encrypted content data for output to an external source. When a license key is to be read out, an encryption communication path is established between the memory card and the dedicated circuit to allow the license key to be transmitted to the dedicated circuit from the memory card via the encryption communication path.
The memory card is also capable of transferring or copying a license with respect to another memory card. In this case, the license is transferred from the source memory card to the destination memory card upon establishing an encryption communication path between the source memory card and the destination memory card, likewise the transmission of a license from a distribution server. Whether the license is to be transferred or copied depends upon the control information included in the license.
The memory card further has the capability to, when the license is lost due to accidental interruption during transmission/reception, recommence the process and record the latest history information associated with license input/output to prevent duplicated transmission, and output the recorded history information, if necessary. The distribution server or memory card that is the transmission source obtains the history information from the destination memory card to determine recommencement of the license transmission/reception according to the obtained history information. The history information includes a license ID and status information indicating reception/transmission.
The user of a terminal device can receive the encrypted content data and license from the distribution server through the communication network, store the received data in a memory card, and then reproduce the encrypted content data stored in the memory card or transfer the stored data to another memory card. Also, the rights of the copyright owner can be protected.
It is to be noted that a conventional memory card stores only the latest history information. In the case where transmission/reception with respect to another license is conducted after an event of communication interruption, the history information as to the previous interruption will be lost. On this occasion, the usability can be improved by storing a plurality of history information.
In accordance with the faster access speed of storage elements, it is expected that the need arises for conducting in parallel a plurality of inputs/outputs of licenses. In this case, there is the necessity to store a plurality of history information associated with respective input/output of license carried out in parallel.
When a license, once stored, is to be transferred to another memory card in the case where a plurality of history information can be stored, two different history information having a different status for the same license ID will be stored, resulting in the event of inconsistency in the stored history information. Thus, there is a possibility of the license being transferred to result in duplication, degrading the security.